Multiphase electric drives are known in which various modulation types are used. Use of pulse width modulation (PWM) in multiphase drives is very common. Multiphase drives of this type are controlled as a function of the particular requirements that are present, according to one of the following methods:                use of sinusoidal current control (sinusoidal commutation),        use of block current control (block energization),        use of block voltages (control with block voltages),        use of sinusoidal voltage control with superimposed zero voltages.        
In principle, the above-mentioned techniques may be used in electric machines having any arbitrary phase number. Electric machines having three phases are most common in practice. However, there are also electric machines having a different phase number, for example two, four, five, six, seven, or nine phases.
In addition, so-called start-stop systems are already known. These systems are used for stopping and restarting an internal combustion engine for the purpose of reducing the fuel consumption and the exhaust gas emissions.
A start-stop system developed by the present applicant operates on the basis of conventional starters. The particular starter is controlled by an electronic control unit, and with the aid of a pinion meshes with a ring gear provided on the flywheel.
Furthermore, it has previously been proposed to implement a belt-driven starter generator on the basis of a claw pole generator, using an additional electronic control unit. In starter generators of this type, the phases are often directly connected to a direct current voltage source such as a battery via electronic semiconductor switches without using a clock method such as PWM.
To be able to recuperate higher amounts of energy in the case of braking, systems having fairly high voltages are necessary. At higher voltages, clocking of the supply voltage in the converter is necessary for starting the internal combustion engine in order to limit the current in the machine to a predefined maximum value. A clocked converter requires a DC link to high-capacitance capacitors in order to smooth the alternating components in the intake current. In the output stages, the dimensioning of the DC links often determines the space requirements for the particular output stage.
As discussed above, in the mentioned machines, types of operations using the clock method (PWM) are used at higher voltages, and types of operations using block commutations (without PWM) are used at lower voltages or at higher rotational speeds. Measuring the current is particularly important in the clock methods, since current control is carried out in these clock methods, for which it is necessary to measure the actual currents.
For measuring the current in the individual phases of the electric machine, either shunt resistors, which convert the current into an equivalent voltage signal, or indirect current measuring methods, such as current transformers or LEM converters, are used.